Ferrule for connecting optical fibers

ABSTRACT

The invention concerns an integrated intermediate ferrule comprising an optical port and optoelectronic circuits functionally interposed between the optical port and an electric port. To avoid having to place a reflecting mirror causing optical losses, the integrated circuit for detection and optoelectronic conversion is arranged perpendicular to a rectilinear path of the light signal in the ferrule. Such an arrangement eliminates the need for a mirror and makes it easy to obtain accurate setting of the alignment of the optical port and the optoelectronic conversion circuits and finally provides efficient cooling of said optoelectronic conversion circuits.

BACKGROUND OF THE INVENTION

1. Field of the Invention

An object of the present invention is a connection ferrule for opticalfibers. It is designed to simplify the use of optical fibers which arean item of increasing utility.

An optical fiber is used essentially as a means to convey information inthe form of light signals that are normally digitized. This means oftransportation has the advantage of efficiently resisting noise,especially electromagnetic noise, and furthermore enabling very highdata bit rates. However, since processing in present-day computerdevices is of the electronic type, it is important to carry out anoptoelectronic conversion of the light signals to be processed at inputand output of the optical fiber. Various solutions have been devised forthese problems of conversion.

2. Description of the Prior Art

Certain solutions have entailed the idea of making harnesses. In theseharnesses, an optical fiber or a bundle of optical fibers is provided,fixedly at one of its two ends (or at least at one of its ends), with anoptoelectronic conversion device. In this case, the optical fiberdelivers electrical signals or electronic signals at one or both endswhile it can deliver optical signals at another end. The drawback ofthis type of solution is, firstly, the cost generated by thisintegration of means. Secondly, the ease with which the fiber can behandled is thereby greatly reduced. Indeed, it will easily be understoodthat the length of the fiber cannot be adjusted as easily as desired,especially if it is provided on either side with electronic conversioncircuits crimped to the ends of the fibers. In this case, it is not atall possible to lengthen or shorten the fiber. All that can be done isto exchange it for another differently sized harness, which however willalso be a high-cost harness. Besides, the presence of the electronicconversion circuit leads to the making of a joining piece at the end ofthe optical fiber. The bulkiness of this joining piece is inconvenientif the fiber has to be threaded into narrow holes to conduct the signalsfrom one place to another.

In other solutions, especially disclosed in the document WO 00/55665, anintermediate ferrule has been devised. This ferrule is designed toenable optical connection and is furthermore provided with integratedoptoelectronic conversion means. However, owing to the chosen techniqueof transmission and the mechanical architecture used to make the device,an optical reflection mirror has to be prepared between the exit of theoptical fibers and an optoelectronic detector or an optoelectronicemitter responsible for making the conversion. Mirror-based approachesof this kind can also be found in the following documents: U.S. Pat. No.5,168,537, U.S. Pat. No. 6,132,107, and U.S. Pat. No. 6,161,965. Thepresence of such mirrors however raises optical and technologicalproblems that impair the efficiency of the optoelectronic conversionundertaken. Indeed, these mirrors imply a specific manufacturingtechnology, need to be aligned and may be the cause of opticaltransmission losses.

At this stage, we are therefore either faced with solutions in which abundle is present, as described for example in the document U.S. Pat.No. 5,416,872, or obliged to resolve the problems of reflection referredto here above.

In the invention, it is planned to overcome these drawbacks by proposinga ferrule capable of receiving detachable ends of optical fibers(normally presented in a standardized joining piece) and capable of alsocarrying out optoelectronic conversion, without furthermore having todeflect the light rays coming from or sent to the optical fibers. Thereceiving of detachable joining pieces in optical port averts theproblem of the bundles. It is enough to have a set of optical fibersections with variable sizes. On the one hand, the joining pieces costlittle to make, and on the other hand their compactness allows them tobe threaded anywhere. The deflection of the light rays is prevented byplacing the useful part of the optoelectronic conversion circuit so thatit directly faces a rectilinear optical path coming from the opticalport.

The ferrule of the invention then has the overall shape of aparallelepiped, of which one of the faces, containing the optical port,is used to receive the detachable ends of the optical fibers, while aface opposite to this receiving face bears an optoelectronic detectionand/or emission circuit as well as a control circuit. Preferably, on aface contiguous to these two faces, the package of the ferrule bearscontacts enabling the connection of this ferrule to an electroniccircuit, especially a printed circuit.

Furthermore, given the difficulties of alignment during the positioningof the optoelectronic detection and/or emission circuit facing theoptical paths thus made (and in which no optical correction is necessaryin principle), a precise positioning is planned using a technique forthe reflow soldering of solder beads. This technique has the advantageof providing for positioning with a precision of about one micrometer.Furthermore, by then preferably making the package of the ferrule out ofplastic, a notable reduction in the cost of the conversion ferrule isachieved.

SUMMARY OF THE INVENTION

An object of the invention therefore is a ferrule for the connection ofoptical fibers comprising an optical port on an input face to detachablyreceive one or more terminations of optical fibers, optoelectroniccircuits for the conversion of optical signals into electrical signalsand/or vice versa, placed on an output face opposite the input face andan electrical port providing connection to an electronic circuit,wherein the ferrule has an optical path leading firstly directly ontothe optical port, and secondly directly onto a detection or emissionpart of the conversion circuits and wherein the electrical port isplaced on a connection face contiguous to the input and output faces.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood more clearly from the followingdescription and the accompanying figures. These figures are given purelyby way of an indication and in no way restrict the scope of theinvention. Of these figures:

FIG. 1 is a view in perspective, seen from underneath, of a connectionferrule according to the invention;

FIG. 2 is a diagrammatic side view of the ferrule of FIG. 1;

FIG. 3 shows a part of the optical fiber connection ferrule of theinvention, before the installation of the optoelectronic conversioncircuits;

FIG. 4 is a diagrammatic view of the preferred mounting of anoptoelectronic integrated circuit in the ferrule of the invention;

FIG. 5 shows dimensions of the ferrule of the invention and presentsimprovements of use;

FIG. 6 shows a particularly useful installation of a heat sink to coolthe optoelectronic conversion circuits.

MORE DETAILED DESCRIPTION

FIG. 1 shows ferrule 1 for connecting optical fibers according to theinvention. This ferrule 1 has an optical port 2 to detachably receiveone or more optical fiber terminations. The optical fibers received are,for example, optical fibers such as 3 provided at their ends with ajoining piece 4 that is preferably standardized. The number of fibers 3may preferably be an even number, with one fiber serving fortransmission in one direction, and another for transmission in anotherdirection. The fibers mounted in a flexible sheet may relate to anyunspecified number of transmission channels, ideally but not solely,four to-and-fro transmission channels. The joining pieces 4 are used toobtain a preset distance between the different terminations of theoptical fibers of a sheet.

The joining piece 4 thus has a face 5 designed to abut a face 6 of theferrule 1. The face 6 is the one comprising the optical port 2. In orderto provide for the precise positioning, to within about one micrometer,of the ends of the optical fibers 3 in the optical port 2, the joiningpiece 4 is provided with pins 8 that get engaged in reserved positionsmade to match in the face 6, also in a very precise manner. The pins 8are used to guide the terminations in the optical port. A package 7 ofthe ferrule 1 is made of insulating material. Preferably, the package 7is molded. Preferably it is made of plastic, for example PBT, LCP orpolyimide which stands up well to temperature, or any other technicalplastic material that stands up to cycles for mounting components byreflow soldering. In the example, the package 7 is furthermoremetallized so as to carry electrical tracks.

The ferrule 1 also has optoelectronic circuits 9 for the conversion ofoptical signals into electrical signals and/or vice versa. In theinvention, the optoelectronic conversion circuits 9, at least detectionand/or emission circuits of these conversion circuits, are placed on aface 10 of the package 7 that is opposite the face 6 by which theoptical fibers have been received. The package 1 has yet anotherelectrical port 11 represented herein by a series of pads formingelevated features on one face 12 of the package 1. The face 12 iscontiguous firstly to the face 10 and secondly to the face 2.

According to an essential characteristic of the invention, shown in FIG.2, the optical signals coming from the optical fibers 3 travel through apreferably rectilinear optical path 13 inside the package 7. They travelbetween the optical port 2, and hence the immediate output of the fiber3, and the conversion circuits 9 at which they produce a direct impactor from which they come out directly, in both cases without reflection.The optical path 13 is given shape, in the package 7 by a material thatis solid, liquid or gaseous and transparent to light rays. To simplifythe explanation, it may be assumed that the package 7 is thus providedwith grooves 13 whose orientation is preferably parallel to the pins 8and is therefore substantially perpendicular to an output face of thejoining piece 4 of the optical fibers 3. These grooves 13 are aligned sothat, at their other end 14, they are placed directly facing andperpendicular to a detection face 15 of the optoelectronic circuits 9.This mode of action makes it clear that it is possible to do without areflection circuit whose drawbacks moreover are known.

Thus, in the event of the use of optical fibers supported in the package7 and serving as an interface between the input face of the package andthe output face of the package to convey optical signals between theoptical port 2 and the optoelectronic components, the holding meansconstituted by the grooves 13 may be rectilinear. In the case of a useof optical waveguides directly made in the package 7, the waveguidesreplacing the interface fibers may be curved, recombined or separated asa function of a desired application.

To make the ferrules of FIGS. 1 and 2, several solutions are possible.These solutions must furthermore comply with certain constraints. As canbe seen in FIG. 2, the optoelectronic detection or emission andsignal-reshaping integrated circuit 9 is, on the whole, mountededgewise, perpendicularly to a printed circuit 16 designed to come intocontact with the electrical port 11. The elevation of the pads 17 sothat they are in relief with respect to the electrical port 11furthermore makes it possible to leave space for a blade of air curtain18, or for any other material, between the integrated circuit 9 andprinted circuit 16 so as to ensure installation and guarantee thereliability of the mounting of the component. As a variant, the contacts17 of the electrical port may also be fixedly joined and electricallyconnected to a connector element, one counterpart element of which isfixedly joined to the printed circuit 16 receiving the ferrule.

For its electrical connection to the printed circuit 16, the integratedcircuit 9 is connected to metallized pins 19 placed on the face 10 ofthe package 2. It is connected to them by solder beads such as 20. Thesolder beads 20 are furthermore connected to connection pins 21 of theintegrated circuit 9 itself.

The technique of setting up an electrical connection of the integratedcircuit 9 by solder beads is a technique known as the flip-chiptechnique, in which a reflow of the solder beads is produced. Inpractice, during manufacture, the integrated circuit 9 is placedhorizontally above the package 7 after the positioning of the solderbeads 20. In this phase, the package 7 is raised vertically with itsface 10 on top. Then the entire piece is taken to a reflow temperatureof over 260 degrees. Then the solder beads 20 achieve firstly theelectrical soldering of the pins 19 to the pins 21. Secondly, throughthe surface tensions that develop in the solder, they provide for anexact positioning of these pins 21 relative to the pins 19.Consequently, if by construction of the integrated circuit 9, the pins21 are positioned precisely relative to the detection or emission ports15 of the electronic circuits 9, and furthermore the pins 19 are placed,by construction, precisely relative to the output hole 14 of therectilinear path 13 in the package 7, then the positioning of theelectronic circuit 9 is obtained quite naturally and with highprecision, in practice with a precision of about one micrometer. We thenhave a configuration in which the alignment is perfect, with awell-mastered technology and hence a low-cost result. At the same time,the assembly could be done otherwise, for example by using a precisepositioning machine.

FIG. 3 shows the making of electrical tracks 22 by which the pins 19 ofthe package can be connected to the pads 17 of the electrical port 11.While the package 7 is preferably made of plastic, the metallized tracks22 may be obtained in different ways. For example, the totality of thepackage is metallized and the tracks 22 are etched thereon, on all itsfaces, by wet etching or by dry etching (by laser). As a variant, it ispossible to carry out a selective etching of the surface of the package7, at the position of the tracks 22, so as to chemically activate thematerial of the service of the package at the position of these tracks7. Then the package is subjected to a chemical metallization, with themetal particles adhering to the zones that have been activated.

It is thus possible to make tracks 22 that spread out not only on oneface 12 of the package containing the pads 17 but also on one or moreother contiguous faces of the package. Furthermore, at the positionwhere there is a change of face, the tracks show electrical continuity.If need be, the ridges 23 between two contiguous faces 10 and 12 may berounded to foster the making of this electrical continuity. As can beseen in FIGS. 2 and 3, the electrical tracks may be of different lengthsaccording to the remoteness of the pad 17 that they connect to the face10.

In the invention, it is noted that the electronic circuit 9 must bepowered electrically, must receive control or signaling signals, andmust transmit signals to be electro-optically converted or that havebeen electro-optically converted. It will then be chosen to reservetracks such as 24 and 25, which have the longest route in the package 7,for carrying electricity. Tracks 26 of intermediate length will be usedfor the transmission of the control or signaling signals, while theshortest tracks 22 will serve for the transmission of the signalsdetected or to be transmitted. In practice, the signals to betransmitted or the converted signals available on the track 22 are veryrapidly variable signals. Their variation depends on the bit rate whichmay be equal to about several gigabits per second. The signals conveyedby the connections 26 are less rapidly variable, for example about oneMHz, while the signals on the connections 24 and 25 are for their partdirect current signals. The tracks 22 and 24 to 26 are preferably madeon the external faces of the package 7.

FIG. 4 is a diagrammatic sectional view of the package 7 as well as theelectronic circuit 9. It furthermore shows that the package 7 is formedby two blocks 27 and 28 joined together. For example, the two blocks 27and 28 are parallelepiped-shaped, like the package 7, and have a height,measured perpendicularly to the printed circuit 16, that is half theheight 29 of the entire package 7. The two blocks 27 and 28 possessmeans to form rectilinear optical paths at the position 30 at which theymeet. In one example, these means are formed by the presence of V-shapedor U-shaped grooves made in at least one of the two blocks 27 or 28, theother block being possibly devoid of grooves and being flat. If desired,these grooves can be used for the positioning of optical fiber sectionstherein or for the deposition therein of a polymer resin playing therole of an optical waveguide so as to make the package 7 transparent tolight at their position. When optical fiber sections or polymerwaveguides are thus placed in the meeting zone 30, a thrust feature 31on the face 10 of the package 7 enables the ends of the sections to bepolished without damage to the metallized tracks.

As a variant, the package is a unique single-piece unit. It is thenpierced with rectilinear holes in which the optical fiber sections orwaveguide are placed or not placed.

The mode of manufacture of the package 7 in two blocks 27 and 28 ispreferred because it enables a simpler making of the rectilinear opticalpaths. The precision of the making of a groove is greater than theprecision of the making of a hole, as the former can be far morerectilinear than the latter. Furthermore, the making of the package intwo blocks permits the making of paths 13 in the form of a materialmolded in the grooves before the blocks are attached together.

Consequently, the metallized tracks such as 24 and 25 each made partlyon each of the blocs are joined, after the two blocks 27 and 28 areattached to each other by electrical bridges such as 32. The electricalbridges are either simple solders, or used to positioning complementarycircuits, especially electrical decoupling circuits, to prevent thetransmission of parasitic electronic signals. The two blocks 27 and 28are joined to each other by bonding or by ultrasonic soldering or bylaser, without or without the presence of optical fibers.

If necessary, at the position of the port 2 and of the optical output14, optical lenses may be placed. Or quite simply, the optical fibersections placed in the holes or in the grooves have rounded shapes attheir ends giving a similar lens effect.

FIG. 4 also shows that the detection or emission and conversionintegrated circuit 9 can preferably be made in the form of twointegrated circuits stacked one on the other. For example, theintegrated circuit 9 has the detection (or emission) circuit proper 33.The circuit 33 is based on VCSEL type diodes. The circuit 9 also has anintegrated analog-digital conversion integrated circuit 34. Theintegrated circuit 34 converts analog electrical signals produced by thedetector 33 into digital electrical signals or vice versa if the circuit33 is an emitter. Preferably, the integrated circuit 33 is connected, bypins not shown, to the integrated circuit 34 by the reflow of solderbeads 35, of the same type as the solder beads 20 so as to ensure aprecise positioning of this integrated circuit 33 relative to theintegrated circuit 34. Since the integrated circuit 34 has itself beingplaced precisely by beads 20 relative to the output 14 of the package 7,the result obtained is that the circuit 33 is placed precisely relativeto the package 7. Given the distances, the solder beads 35 will be farsmaller than the solder beads 20 so that the integrated circuit 33 canfind a place in a gap 36 made between the face 10 of the package 7 andthe integrated circuit 34. Typically, the space between the surface 15and the face 10 is 100 micrometers.

FIG. 5 shows the overall dimensions of the unit formed by the package 7and the optoelectronic integrated circuit 9. In practice, a ferrulemodule according to the invention will have the following dimensions,plus or minus 10%: a length of 5 mm, a width of 7 mm and a height of 2mm. It will be noted that this height of 2 mm is quite compatible withassembly on a printed circuit 16, and permits the attachment of severalprinted circuit boards 16 mounted edgewise and placed against oneanother. FIG. 5 also shows that it is possible to use an upper face 37of the package 7, opposite the face 12 bearing the electrical port 11,to position other integrated circuits such as 38 in a position ofinterconnection between or on electrical linking tracks. The circuit 38will preferably be a passive type circuit, mounted according to an SMC(surface-mounted component) type of technology.

FIG. 6 gives a diagrammatic view of the package 7 connected to anelectronic circuit 9. The electronic circuit 9 has a flat conversioncircuit 34 whose surface is substantially parallel to the output face 10of the package 7. This construction then permits the positioning of asink 39 placed flat against the back of the integrated circuit 34, forexample by means of a thermal transmission bonder 40. Indeed, it can beestimated that an optoelectronic conversion circuit working at very highspeed to ensure the bit rate transmitted by the optical fiber is anelement that produces a substantial quantity of heat. The fact of havingplaced the integrated circuit 34 edgewise, perpendicularly to a printedcircuit 16 (not shown) then makes it possible to place the sink 39usefully with its thermal connector plate perpendicular to the printedcircuit 16.

In a commercially distributed version, this set is placed in a holdingcase 41. The holding case 41 possesses, firstly, the optical port 2 and,secondly, the optical port 11, both being placed on faces that areperpendicular to the package 7.

It is possible to install a certain number of emitter/receiver pairsmade in one or more integrated circuit such as 9 mounted on the face 10and connect them to the pins such as 19.

The large number of pads such as 17 enables the package to be held onthe circuit 16. If need be, some of them are not functional for makingelectrical links.

1. Ferrule for the connection of optical fibers comprising an opticalport on an input face to detachably receive one or more terminations ofoptical fibers, optoelectronic circuits for the conversion of opticalsignals into electrical signals and/or vice versa, placed on an outputface opposite the input face and an electrical port providing connectionto an electronic circuit, characterized in that the ferrule has anoptical path leading firstly directly onto the optical port, andsecondly directly onto a detection or emission part of the conversioncircuits and in that the electrical port is placed on a connection facecontiguous to the input and output faces.
 2. Ferrule according to claim1, characterized in that the optical path is formed in a packagecomprising the input face provided with the optical port, the outputface bearing at least one part of the optoelectronic circuits and theconnection face comprising contacts of the electrical port.
 3. Ferruleaccording to claim 1, characterized in that the optical path isrectilinear.
 4. Ferrule according to claim 2, characterized in that thepackage comprises electrical tracks on its external faces to connect theoptoelectronic circuit to the contacts of the electrical port. 5.Ferrule according to claim 2, characterized in that the optoelectroniccircuit is connected to the tracks of the package by operations ofreflow of solder beads.
 6. Ferrule according to claim 2, characterizedin that electrical tracks made in the package to connect theoptoelectronic circuit to the contacts of the electrical port comprisefirst DC electrical power supply tracks and second tracks taking a routein the package that is shorter than the first tracks.
 7. Ferruleaccording to claim 2, characterized in that the package is made out oftwo blocks joined by a common face, the region in which the blocks meetcomprising optical paths, and electrical bridges being made for thecontinuity of the electrical tracks located in part on one block and inpart on another block.
 8. Ferrule according to claim 2, characterized inthat the package is made of an insulating material, molded andmetallized to carry electrical tracks.
 9. Ferrule according to claim 1,characterized in that the optical path is formed by a solid materialtransparent to light rays.
 10. Ferrule according to claim 1,characterized in that the contacts of the electrical port are formed bymetallized pads.
 11. Ferrule according to claim 1, characterized in thatthe optoelectronic circuit comprises a first integrated circuit for theconversion of electrical signals and a second integrated circuit foroptical detection and/or emission, the second integrated circuit beingmounted on and being connected with the first integrated circuit byoperations of reflow of solder beads.
 12. Ferrule according to claim 1,characterized in that the optical port comprises means to preciselyguide optical terminations in the optical port.
 13. Ferrule according toclaim 1, comprising a sink characterized in that the optoelectroniccircuit comprises a first integrated circuit for the conversion ofelectrical signals, this first integrated circuit being placed incontact with the sink.
 14. Ferrule according to claim 1, characterizedin that the optoelectronic circuit comprises a first integrated circuitfor the conversion of electrical signals, this first integrated circuitbeing placed perpendicularly to a printed circuit receiving the ferrule.